Unnecessary use of the anthrax antibiotic ciprofloxacin could undermine the effectiveness of the drug, an expert has warned.

It may also compromise the effectiveness of other antibiotics used to treat a range of disease.

There is growing evidence that many people in the US are ignoring public health messages and stocking up on the powerful antibiotic.

If we have hundreds of thousands of people taking antibiotics unnecessarily we are going to see resistant strains

Dr Richard Corlin

Some US residents worried about the threat of anthrax are heading to Mexico, where antibiotics are cheaper and prescriptions are not needed.

The drug can also be easily purchased on the web from foreign manufacturers.

Dr Richard Corlin, president of the American Medical Association (AMA), said that widespread use of Cipro would increase the possibility that anthrax spores would develop resistance to the drug.

He said: "If we have hundreds of thousands of people taking antibiotics unnecessarily we are going to see resistant strains, and it is not just anthrax, we are going to see resistant strains of other organisms."

Dr Corlin accused people who were making Cipro available to the public of "cashing in".

He said: "Whether they are physicians, pharmacists, or business people, we do wish they would stop because they are hurting the public."

Side effects

Cipro is a powerful drug that is not recommended for use by children.

It can produce a number of unpleasant side effects. These include:

damage to the central nervous system such as dizziness, confusion, tremors, hallucinations, depression and increased risk of seizures

an allergic reaction which can produce difficulty breathing; closing of the throat; swelling of the lips, tongue, or face and hives